Ray Donovan, the US special agent who obsessively pursued 'Chapo'

Ray Donovan, the US DEA chief in New York who obsessively pursued now-imprisoned drug baron Joaquin "El Chapo" Guzman

Seven years ago, US special agent Ray Donovan began an in-depth study of the Joaquin "El Chapo" Guzman saga -- and it quickly became an obsession.

Now, the tall, 48-year-old New Yorker displays behind glass in his office the beige T-shirt that prisoner 3912 -- Guzman, the former head of the Sinaloa cartel -- wore when he was extradited from Mexico to the United States on January 19, 2017.